JPH06262377A - Method for controlling welding state of laser beam welding and welding condition - Google Patents

Abstract

PURPOSE:To accurately determine the welding state and welding condition by irradiating materials to be welded with a laser beam to monitor plasma generated from a weld zone and further, calculating the whole plasma intensity. CONSTITUTION:A computer 10 takes in output of photosensors 4 and 5 monitoring laser beam induced plasma P on the front and rear surfaces of the weld zone B in a specified period and determines whether or not generation of the laser beam induced plasma P is recognized on the rear side of the materials W to be welded based on output of the rear side photosensor 5. When penetration is not penetrated up to the rear side of the materials W to be welded, a next step is proceeded. When penetration is pierced up to the rear side of the materials W to be welded, output of the rear side photosensor 5 is corrected and the whole plasma intensity is calculated. A value of this whole plasma intensity is compared with a reference value and when it is deviated from the proper range, it is considered that excess and deficiency are caused on penetration of base matals, welding error processing is executed and welding is stopped at the point of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing the welding state and welding conditions of laser welding, and more particularly to managing the welding state and welding conditions by monitoring the plasma generated by laser light generation with an optical sensor. On how to do.

[0002]

2. Description of the Related Art In laser welding of steel sheets and the like, in order to manage the welding state (welding quality) such as the penetration depth of the welded portion, the plasma induced by the laser light is monitored by an optical sensor. There is a way.

FIG. 11 is a diagram showing an example of the conventional control method, in which CO ₂ and Y are applied to the objects W to be welded which are superposed on each other.
Laser light L output from a laser oscillator 1 such as AG is condensed by a condensing optical system 2 such as a lens and then irradiated, and welding is performed while the workpiece W and the laser light L are relatively moved at a predetermined speed. On the other hand, an optical sensor 51 such as a phototransistor or the like which directs the welding portion B is arranged above the workpiece W, and the intensity of the plasma P generated in the welding portion B induced by the laser light L is detected by the optical sensor. It is what is monitored by 51. The detection output of the optical sensor 51 is processed by the signal processing device 52 and compared with a preset reference value to determine whether or not the penetration depth of the welded portion B is appropriate.

The laser-induced plasma P is generated by vaporization and ionization of the base material.
Has the property of absorbing well. Then, as shown in FIG. 10, although the plasma P ₁ having a relatively high density in the keyhole H of the welded portion B absorbs the laser light L as described above, it contributes to an increase in the penetration depth. Welded part B
If a large amount of plasma P ₂ having a relatively low density floats above, the laser beam L will be absorbed first and the effective welding energy density at the welded portion B will be lowered, and therefore, FIG. As shown in FIG. 3, an inert gas G such as helium or argon is obliquely blown from the nozzle 3 toward the welded portion B to eliminate the above-mentioned relatively low-density plasma P ₂ .

[0005]

In the conventional management method as described above, the total plate thickness of the workpiece W is relatively large (for example, 2 mm or more), and the penetration depth is set on the back surface of the workpiece W. If the penetration penetrates to the back surface side of the workpiece W under the condition of the limit of whether or not the laser-induced plasma P is partially penetrated, as shown in FIG. It will also be ejected from the back side of the object W. As a result, the amount of light received by the optical sensor 51 that monitors the laser-induced plasma P on the surface side of the workpiece W decreases, and the welding state (penetration depth) using the laser-induced plasma P as a medium can be accurately determined. You can't do it.

Further, as described above, the laser-induced plasma P
When the welding conditions such as the laser output and the flow rate of the inert gas are simultaneously controlled by monitoring the above, the emission intensity of the laser-induced plasma P is affected by the composite of the above welding conditions. As shown in FIG. 11, it is not possible to accurately determine whether each welding condition is within the proper range by only using the single optical sensor 51.

That is, the received light amount characteristic received by the optical sensor 51 of FIG.
Is affected by the depression angle θ (the angle between the pointing direction of the optical sensor 51 and the workpiece W) θ, and the optimum depression angle θ is different for each welding condition. The suitability of each welding condition cannot be accurately determined only by 51.

As shown in FIG. 10, this is a plasma P having a high density and a high emission intensity in the keyhole H of the welded portion B.
₁ and the degree of visibility of the plasma P ₂ having a relatively low density and a small emission intensity above the keyhole H is the optical sensor 51 of FIG.
It depends on the depression angle θ of the
The plasma P ₂ having a relatively low density and a small emission intensity in the upper portion is greatly affected by the flow rate of the inert gas, while the plasma P ₁ having a high density and a large emission intensity in the keyhole H is changed by the flow rate of the inert gas. Has the property that it is not so affected.

The present invention has been made by paying attention to the above-mentioned conventional problems, and has an effect on jetting characteristics of laser-induced plasma from the back surface of the object to be welded and on the received light amount characteristic due to the difference in the depression angle of the optical sensor. In view of the above, it is an object of the present invention to provide a method capable of accurately determining a welding state and welding conditions.

[0010]

According to the invention of claim 1 of the present application, when an object to be welded is irradiated with a laser beam for welding, plasma generated by the laser beam from a welding site is induced by an optical sensor. In the method of monitoring and managing the welding state based on the intensity of the laser-induced plasma,
Individually monitor the generation of laser-induced plasma on the front and back both sides of the welded portion by the optical sensor disposed on the front and back both sides of the object to be welded, if the output value of the optical sensor on the back side is less than a predetermined value, While comparing the output value of the optical sensor on the front side with a reference value preset as the total plasma intensity to determine the adequacy of the welding state, when the output value of the optical sensor on the back side is a predetermined value or more, The total plasma intensity is calculated by multiplying the output value of the optical sensor on the back side by a predetermined correction coefficient, and then added to the output value of the optical sensor on the front side, and the total plasma intensity is compared with the reference value. It is characterized in that the suitability of the welding state is determined by using.

According to the second aspect of the present invention, when laser welding is performed while irradiating an object to be welded with laser light and spraying an inert gas onto the welding site, plasma generated from the welding site is induced by the laser beam. In a method of controlling a plurality of welding conditions such as laser output and inert gas flow rate based on the intensity of the laser-induced plasma by monitoring an optical sensor, and a different depression angle that directs the welding site from above the workpiece. The generation of laser-induced plasma at the welding site is individually monitored by a plurality of optical sensors, and the items of the welding conditions to be managed by each of the optical sensors are set in advance for each of the optical sensors. The relationship between the variation of the data and the output of the corresponding optical sensor is defined as correlation data in advance, and the output of each of the optical sensors during welding is applied to the corresponding phase. Welding condition data corresponding to each optical sensor output is individually calculated by collating with the data, and the calculated welding condition data is compared with a preset reference value to determine the suitability for each welding condition. It is characterized by doing.

[0012]

According to the first aspect of the present invention, when the penetration due to the laser welding reaches the back side of the object to be welded and the laser-induced plasma is ejected to the back side as well, the output value of the optical sensor on the back side is corrected to a predetermined value. By multiplying by the coefficient and adding it to the output value of the optical sensor on the front surface side to calculate the total plasma intensity, it becomes possible to determine the adequacy of the welding state in consideration of the plasma ejection amount on the back surface side.

According to the second aspect of the invention, an optical sensor having an optimum depression angle for each welding condition to be controlled is provided to monitor the laser-induced plasma. The suitability can be determined.

[0014]

FIG. 2 is a diagram showing a first embodiment of the present invention, and shows an example in which the welding state (penetration depth) is controlled by monitoring the laser-induced plasma P as in FIG.
The same parts as those in FIG. 11 are designated by the same reference numerals.

As shown in FIG. 2, apart from the optical sensor 4 which is provided on the front surface side (upper part) of the workpiece W and points the weld portion B, the weld portion B is also formed on the rear surface side of the workpiece W. It is different from the conventional one in that an optical sensor 5 for directing is provided.

The outputs of the optical sensors 4 and 5 are amplified by amplifiers 7A and 7B of the signal processing device 6, respectively, and then high-frequency component noises are removed by filters 8A and 8B, and A / D converter 9A and After being A / D converted by 9B, it is taken into the computer 10. Then, by comparing the output of each of the optical sensors 4 and 5 with a reference value stored in advance in the memory of the computer 10, it is possible to determine whether the welding state is appropriate or not.

FIG. 3 shows the change of the focal position when the position of the focal point, which is one of the welding conditions, is changed and the respective optical sensors 4, 4.
5 shows the relationship with the change in the amount of received light of No. 5. In addition,
The welding conditions are a laser output of 2.5 kW, an argon (Ar) gas supply rate of 20 liters / min, which is an inert gas, and a welding speed of 2.5 m / min.

As shown in FIG. 3, when the focal position is in the range of about -1 mm to +2 mm near the in-focus position, the penetration of the base metal at the welded portion B extends to the back surface of the workpiece W and is substantially the same. Since it penetrates, the output Q _{2 of the} photosensor 5 on the back side is large due to the jetting of the laser-induced plasma P to the back side, and the output Q _{1 of the} photosensor 4 on the front side becomes relatively small during that time. You can see that In other words, when the laser-induced plasma P is observed on the back surface side of the workpiece W, it means that the emission intensity of the laser-induced plasma P, which can be observed on the front surface side, decreases.

However, the optical sensors 4 and 5 differ in the distance from the laser-induced plasma P and the observation angle, and when obtaining the total plasma intensity Q, the optical sensors 4 and 5 are obtained.
It does not make sense to simply add the outputs Q ₁ and Q ₂ of 5. Therefore, under exactly the same conditions as in the case of FIG. 3, using a workpiece to be welded that is thick enough that the penetration does not penetrate to the back surface side, the change in the output of the optical sensor 4 on the front surface side when the penetration does not penetrate to the back surface side, that is, The change in the total plasma intensity Q was obtained as shown in FIG. Then, each of the optical sensors 4 in FIG.
The correction coefficient Z such that the sum of the output characteristics Q ₁ and Q ₂ of _No. 5 becomes the total plasma intensity characteristic Q of FIG. 4 was obtained by the following equation.

Q = Q ₁ + Z · Q ₂ (1) That is, the correction coefficient Z is obtained as a function of Q ₂ as shown in FIG. 5 as a value of Q = Q ₁ + Z · Q ₂ . .

By using this correction coefficient Z, the laser-induced plasma P is generated by the optical sensors 4 and 5 on both the front surface side and the back surface side even under the condition that the penetration by welding reaches the back surface of the workpiece W. By monitoring
Appropriateness of the welding state (melting state) of the laser welded portion B can be accurately determined. This is the same under welding conditions other than the focus position shown in FIGS.

FIG. 1 is a diagram showing a processing procedure in the system shown in FIG. 2. In the memory of the computer 10 shown in FIG. 2, the value of the correction coefficient Z and the reference value Q ₀ of the total plasma intensity are stored and set in advance. Has been done.

First, as shown in FIG. 1, when welding is started, the computer 10 outputs the outputs Q ₁ , from the optical sensors 4 and 5 that monitor the laser-induced plasma P on both front and back surfaces of the welded portion B. Q ₂ is taken in at a constant cycle (step S in FIG. 1).
1 to S4), based on the output Q ₂ of the optical sensor 5 on the back surface side, whether or not the generation of the laser-induced plasma P is recognized on the back surface side of the workpiece W, that is, the penetration by welding is It is determined whether or not it penetrates to the back surface side (step S5).

When the penetration has not penetrated to the back surface side of the workpiece W, the total plasma intensity Q = Q ₁ is set and the process proceeds to the next step (step S7). When penetrating to the back surface side, the output Q ₂ of the photo sensor 5 on the back surface side is corrected by Q = Q ₁ + Z · Q ₂ to calculate the total plasma intensity Q (step S6).

Further, regardless of whether the penetration of the base material by welding penetrates to the back surface side of the workpiece W,
The value of the above-mentioned total plasma intensity Q is compared as a preset reference value Q ₀ , and it is judged whether or not it is within an appropriate range (step S8). As long as the above-mentioned total plasma intensity Q is appropriate, The above series of steps is repeated until the welding is completed (steps S9 and S10).

On the other hand, when it is determined in step S8 that the total plasma intensity Q deviates from the proper range, it is considered that there is an excess or deficiency in the penetration of the base metal, and the welding error processing is performed. After that, the welding is stopped at that point (step S11).

As described above, according to this embodiment, the workpiece W is welded.
By calculating the total plasma intensity Q in consideration of the laser-induced plasma P generated on the back surface side of the, and comparing the total plasma intensity Q with a preset reference value Q ₀ , the suitability of the penetration depth is determined. , The penetration depth can be accurately determined even in the case of welding under the condition where the penetration reaches or does not reach the back surface side of the workpiece W, and the reliability of the determination result is greatly improved. improves.

FIG. 6 is a diagram showing a second embodiment of the present invention.
An example of managing welding conditions such as laser output and inert gas flow rate by monitoring the laser-induced plasma P is shown. The same parts as those in FIG. 2 are designated by the same reference numerals.

As shown in FIG. 6, above the work W to be welded, the depression angles θ ₁ and θ _{2 of the} welded portions B are oriented while pointing toward each other.
2 is provided in that two different optical sensors 11 and 12 are provided. The depression angle θ ₂ of one optical sensor 12 is 30 degrees, and the depression angle θ ₁ of the other optical sensor 11 is 60 degrees.
Each time it is set.

Outputs S ₁ and S of the optical sensors 11 and 12
₂ is an amplifier 7A, 7B, a filter 8A, 8B and A
After being taken into the computer 10 via the D / D converters 9A and 9B and compared with a reference value stored in advance in the memory of the computer 10, the welding conditions such as the laser output and the inert gas flow rate can be determined. Adequacy judgment will be made individually for each welding condition.

FIG. 7 shows changes in the laser output when the laser output, which is one of the welding conditions, is changed, and the respective optical sensors 11,
12 shows the relationship with the change in the amount of received light (light sensor outputs S ₁ , S ₂ ), and FIG. 8 shows the change in the flow rate when the flow rate of the inert gas G is changed and the change in the amount of received light of each of the optical sensors 11, 12. It shows the relationship with.

As is apparent from FIG. 7, when the laser output is changed, one optical sensor 11 having a depression angle of 60 degrees is used.
Of the optical sensor 12 having a depression angle of 30 degrees changes little with the change of the laser output, while the output of the other photosensor 12 hardly changes with the change of the laser output. As shown in FIG. 10, the depression angle θ ₁ of one optical sensor 11 is larger than that of the other optical sensor 12, and the keyhole H
Since the deep portion of the laser is observed, the laser-induced plasma P inside the keyhole H that changes according to the laser output.
_This is because changes in ₁ can be sensitively captured. On the other hand, the other optical sensor 12 observes the upper part of the keyhole H more than the optical sensor 11 because the depression angle θ ₂ is small, and the emission intensity of the laser-induced plasma P _{2 on} the upper part of the keyhole H. This is because the density of the plasma itself is small, and therefore the laser output does not change significantly for changes in the laser output.

On the other hand, as shown in FIGS. 8 and 10, the output S ₁ of the optical sensor 11 having a depression angle of 60 degrees is hardly affected by the change in the flow rate of the inert gas blown from the nozzle 3, while The output S ₂ of the optical sensor 12 is influenced by the laser-induced plasma P ₂ above the keyhole H due to the increase / decrease in the flow rate of the inert gas because the laser-induced plasma P ₂ above the keyhole H is observed to a large extent. Therefore, it changes greatly in accordance with the change in the flow rate of the inert gas.

Therefore, although the optical sensors 11 and 12 of FIG. 6 both monitor the laser-induced plasma P of the welded portion B, the laser output is controlled by the output of one optical sensor 11 and the other optical sensor is controlled. In order to control the flow rate of the inert gas by the output of 12, the characteristic curve S ₁ of FIG. 7 and the characteristic curve S ₂ of FIG. 8 are stored in the memory of the computer 10 in advance as correlation data.

FIG. 9 is a diagram showing a processing procedure in the system shown in FIG. 6. When welding is started, the computer 10
The outputs S ₁ and S ₂ of both optical sensors 11 and 12 which monitor the laser-induced plasma P at the welded portion B are taken in at a constant cycle.

That is, first, the output S ₂ of one optical sensor 12 is taken into the computer 10 (steps S1 to S3 in FIG. 9) and compared with the correlation data in FIG. 8 stored in the memory of the computer 10 in advance. Then, the inert gas flow rate Q _G corresponding to the output S ₂ of the optical sensor 12 is calculated (step S ₄ ).

Then, the calculated inert gas flow rate Q _G
And a reference gas flow rate Q _G0 stored in advance in the computer 10 are compared to determine whether or not the inert gas flow rate Q _G is within an appropriate range (step S5). Execution result, if the inert gas flow rate Q _G is proper range shifts to the next step, while the inert gas flow rate Q _G is the error processing of the inert gas flow rate if departing from the proper scope of determination Then, the welding is stopped at that point (step S7).

Further, in step S6 of FIG. 9, the output S ₁ of the other photosensor 11 is fetched into the computer 10 and compared with the correlation data of FIG. A laser output W _L corresponding to the output S _{1 of the} sensor 11 is calculated (step S
7).

Then, the calculated laser output W _L and
The reference laser output W _L0 stored in advance in the computer 10 is compared to determine whether or not the laser output W _L is within an appropriate range (step S).
8). As a result of the determination, if the laser output W _L is within the proper range, the above series of steps are repeated until the welding is completed (steps S9 and S10). On the other hand, if the laser output W _L deviates from the proper range, the laser is released. Error processing of the output W _L is executed, and welding is stopped at that point (step S1).
1).

As described above, by individually monitoring the laser-induced plasma P with the optical sensors 11 and 12 having different depression angles for each welding condition of the inert gas flow rate Q _G and the laser output W _L , each welding condition can be determined. It can be independently determined whether it is within the proper range.

In both the first and second embodiments, the feedback is directly applied to the laser output control system and the inert gas flow rate control system so that the corresponding welding condition falls within the proper range as the error processing. You may do it.

[0042]

As described above, according to the invention of claim 1,
In addition to the front side optical sensor that monitors the laser-induced plasma on the front side of the work piece, a back side optical sensor that monitors the laser-induced plasma on the back side of the work piece is provided. The output value is multiplied by a predetermined correction coefficient and then added to the output value of the optical sensor on the surface side to calculate the total plasma intensity, and this total plasma intensity is compared with a reference value to determine the adequacy of the welding state. By doing so, when the setting of the penetration depth of the welded portion is under the condition where it penetrates to the back surface of the welded object or just under the condition, the penetration penetrates to the back surface side of the welded object. Even in this case, the welding state can be accurately determined in consideration of the generation of laser-induced plasma on the back surface side, and the reliability of the determination result is improved.

According to the second aspect of the present invention, the laser-induced plasma is individually monitored by the photosensors having different depression angles for each welding condition, and the output value of the photosensor and the welding condition data stored in advance are stored. By calculating the corresponding welding condition data from the correlation data and comparing it with the reference value to judge the suitability of each welding condition, it is possible to accurately judge the suitability of each welding condition for multiple welding conditions. , The reliability of the determination result is improved.

[Brief description of drawings]

FIG. 1 is a flowchart of a processing procedure showing a first embodiment of the present invention.

FIG. 2 is a schematic explanatory diagram of a system that executes the processing procedure of FIG.

FIG. 3 is a characteristic diagram showing a correlation between a focus position of laser light and an output of an optical sensor.

FIG. 4 is a characteristic diagram showing a correlation between a focus position of laser light and an output of an optical sensor.

5 is an explanatory diagram of a correction coefficient required to make the two characteristics of FIG. 3 into the characteristics of FIG.

FIG. 6 is a schematic explanatory diagram of a system showing a second embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a correlation between a laser output and an optical sensor output.

FIG. 8 is a characteristic diagram showing a correlation between an inert gas flow rate and an optical sensor output.

9 is a flowchart showing a processing procedure in the system of FIG.

FIG. 10 is a cross-sectional explanatory view of a welded portion.

FIG. 11 is a schematic explanatory diagram of a conventional welding state management system.

12A and 12B are cross-sectional explanatory views of a welded portion, where FIG. 12A is a cross-sectional explanatory view when the penetration does not reach the back surface, and FIG. 12B is a cross-sectional explanatory view when the penetration reaches the back surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser oscillator 2 ... Condensing optical system 4, 5 ... Optical sensor 6 ... Signal processing apparatus 10 ... Computer 11, 12 ... Optical sensor B ... Welding part G ... Inert gas L ... Laser light P ... Laser induced plasma W ... Workpiece

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G07C 3/00 9146-3E

Claims (2)

[Claims] 1. When irradiating a workpiece with laser light to perform welding, plasma generated by the laser light at a welding site is monitored by an optical sensor, and welding is performed based on the intensity of the laser-induced plasma. In the method of managing the state, the generation of laser-induced plasma on the front and back surfaces of the welding site is individually monitored by the optical sensors arranged on the front and back surfaces of the workpiece, and the output value of the back side optical sensor is predetermined. If the value is less than the value, the output value of the optical sensor on the front surface side is compared with a reference value preset as the total plasma intensity to determine whether the welding state is appropriate, while the output value of the optical sensor on the rear surface side is a predetermined value. In the above case, the output value of the optical sensor on the back surface side is multiplied by a predetermined correction coefficient and then added to the output value of the optical sensor on the front surface side to calculate the total plasma intensity. Previous A welding state management method for laser welding, characterized in that the appropriateness of the welding state is determined by comparing with a reference value. 2. When performing laser welding while irradiating a workpiece with a laser beam and spraying an inert gas onto the welded part, plasma generated by the laser beam at the welded part is monitored by an optical sensor, In a method of controlling a plurality of welding conditions such as a laser output and an inert gas flow rate based on the intensity of the laser-induced plasma, the welding is performed by a plurality of optical sensors having different depression angles that direct the welding site from above the workpiece. Individually monitor the generation of laser-induced plasma in the site, while predetermining the welding condition items to be managed by each optical sensor for each optical sensor, the variation of the data of each welding condition and the corresponding The relationship between the output of each optical sensor is specified in advance as correlation data, and the output of each optical sensor during welding is compared with the corresponding correlation data. It is characterized in that welding condition data corresponding to each optical sensor output is individually calculated, and each of the calculated welding condition data is compared with a preset reference value to determine suitability for each welding condition. Welding condition management method for laser welding.